Seamless mobility in wireless networks

ABSTRACT

AP&#39;s associated with a communication network and any wireless devices desiring contact, operated according to a protocol in which each wireless device selects AP&#39;s with which to communicate. A system coordinator causes the AP&#39;s to operate so as to guide each wireless device to an AP selected by the system coordinator. This has the effect that, notwithstanding that the protocol involves having the wireless device make the selection of AP, functionally, the AP&#39;s make the selection for it. In a 1 st  technique, multiple AP&#39;s share an identifier, with the system coordinator directing one particular AP to respond to the wireless device, thus appearing to wireless devices as a “personal cell”. In a 2 nd  technique, AP&#39;s each maintain identifiers substantially unique to each wireless device, with the system coordinator directing only one particular AP to maintain any particular wireless device&#39;s identifier, thus appearing to wireless devices as a “personal AP”.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of the following document(s),collectively sometimes referred to herein as the “IncorporatedDisclosure”. Each of these documents forms a part of this disclosure,and is hereby incorporated by reference as if fully set forth herein.

-   -   U.S. patent application Ser. No. 11/715,287 filed Mar. 7, 2007,        in the name of inventors Vaduvur Bharghavan, Sung-Wook Han,        Joseph Epstein, Berend Dunsbergen, and Saravanan        Balasubramanian, assigned to the same assignee, titled “Seamless        Mobility in Wireless Networks,”, now allowed, which is a        continuation of U.S. patent application Ser. No. 11/298,864,        filed Dec. 9, 2005, in the name of the same inventors, assigned        to the same assignee, and under the same title, now abandoned.    -   U.S. patent application Ser. No. 11/294,673, filed Dec. 5, 2005,        in the name of inventors Rajendran Venugopalachary, Senthil        Palanisamy, Srinath Sarang, and Vaduvur Bharghavan, and assigned        to the same assignee, titled “Omni-Directional Antenna        Supporting Simultaneous Transmission and Reception of Multiple        Radios with Narrow Frequency Separation,”, now pending.

BACKGROUND OF THE INVENTION

In wireless communication, devices send and receive messages withoutbeing physically coupled. Wireless devices can include portablecomputers, telephones, location sensors (such as those using GPS), andthe like. Portable computers with wireless communication capability canbe coupled to a computer network, such as the Internet or the World WideWeb. The IEEE 802.11 standard (including 802.11a, 802.11b, and 802.11g)is one known technique for coupling wireless devices to a computernetwork. In 802.11, wireless devices seek out and select “access points”(herein sometimes called “AP's”), which are themselves physicallycoupled, for computer communication, to at least a system coordinator.Each wireless device associates itself with a particular AP, with whichit communicates. Each wireless device (which might be moving) determinesfrom time to time if it has good communication with its associated AP,and whether it would have better communication with a different AP. EachAP might be coupled to a single device, a collection of devices, or to acomputer network.

In any of these cases, the known art exhibits several problems:

One problem is that handoff (deassociating a wireless device from a1^(st) AP, and associating that wireless device with a 2^(nd) AP) cantake substantial time in relation to the communication. This mightconstrict the wireless devices and AP's from using their fullcommunication ability. This might also reduce the ability of AP's toprovide QoS guarantees that are needed for some uses of wirelessdevices, such as VoIP and other voice or video applications.

A second problem is that each wireless device chooses the AP itassociates with, based only on local state visible to the device. Thismight create a system of device-to-AP associations that results insub-optimal usage of the wireless spectrum. This might result in lowerperformance not only for the wireless device that makes the sub-optimalassociation decision, but for the network as a whole, since wireless isa shared medium.

SUMMARY OF THE INVENTION

The invention includes a set of communication links between AP'sassociated with a communication network and any wireless devicesdesiring contact with that communication network, in which thosecommunication links are operated according to a protocol in which eachwireless device selects AP's with which to communicate. This protocol ispreferably IEEE 802.11, but might be any other protocol with thisproperty or of this kind. The system coordinator causes the AP's tooperate so as to guide each wireless device to an AP selected by thesystem coordinator. This has the effect that, notwithstanding that theprotocol involves having the wireless device make the selection of AP,functionally, the AP's make the selection for it.

In a 1^(st) way to perform this function, multiple AP's share anidentifier (preferably a BSSID, but other unique identifiers might beused), with the system coordinator directing one particular AP torespond to the wireless device. Since each AP uses the same BSSID torespond to the wireless device, the wireless device cannot tell which APit is communicating with. This has the effect that the systemcoordinator can move the wireless device's association with an AP from a1^(st) to a 2^(nd) AP, both without knowledge by the wireless device andwithout the delay introduced by a handoff operation. This also has theeffect that the collection of AP's appears to the wireless device as ifthey collectively form a single cell for communication, personal to thatwireless device.

In a 2^(nd) way to perform their function, AP's each maintainidentifiers substantially unique to each wireless device (preferablyBSSID's, but other identifiers might be used), with the systemcoordinator directing only one particular AP to maintain any particularwireless device's identifier. This has the effect that the systemcoordinator can move the wireless device's association with an AP from a1^(st) to a 2^(nd) AP, both without knowledge by the wireless device andwithout the delay introduced by a handoff operation. This also has theeffect that the collection of AP's appears to the wireless device as ifthere is only a single AP, personal to that wireless device.

In IEEE 802.11, each AP sends a beacon advertising its presence, andwireless devices can decide to respond to that beacon. When AP's havemultiple identifiers to advertise, the AP can collect those multipleidentifiers into a single beacon. This has the effect that the AP cansend fewer beacons. The AP can also send those individual or aggregatedbeacons at a relatively higher data rate, with the effect that thebeacon does not last any longer for multiple identifiers than for asingle identifier.

In cases in which the protocol indicates that the wireless devicechooses parameters for communication with the AP (as in IEEE 802.11 andin other protocols), the AP can customize its beacon relative to eachidentifier, with the effect that the AP can force the wireless device toselect from communication parameters preferred by the AP (or the systemcoordinator). The AP might even restrict the wireless device to only asingle set of communication parameters, with the effect of not givingthe wireless device any effective choice. In a preferred embodiment,those communication parameters might include parameters for accesscontrol, backoff or retry parameters, channel selection parameters,quality of service, transmit power, or some combination of them.

There is no particular requirement that handoff operations must involveactual movement of wireless devices; instead, handoff operations mightoccur between co-located APs. This has several salutary effects, atleast some of which are as follows. (1) The system coordinator canrespond to changed communication conditions by balancing loads betweenAP's, for example co-located AP's or AP's with overlapping effectiveranges. (2) Load balancing can be performed transparently to thewireless device, even within a single channel, without delays associatedwith hard handoffs to different APs. (3) Each AP can operatesimultaneously to maximize data rate and throughput while minimizingsubstantial interference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a wireless communication systemincluding access points and wireless devices.

FIG. 2 illustrates one embodiment of a personal cell model for awireless communication system.

FIG. 3 illustrates one embodiment of a personal access point model for awireless communication system.

FIGS. 4 and 5 show data structures used for a personal access pointmodel for a wireless communication system.

FIGS. 6 and 7 show conceptual diagrams of two cases that can result inhard handoffs between wireless devices using personal access points.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Generality of theDescription

This application should be read in the most general possible form. Thisincludes, without limitation, the following:

-   -   References to specific structures or techniques include        alternative and more general structures or techniques,        especially when discussing aspects of the invention, or how the        invention might be made or used.    -   References to “preferred” structures or techniques generally        mean that the inventor(s) contemplate using those structures or        techniques, and think they are best for the intended        application. This does not exclude other structures or        techniques for the invention, and does not mean that those        structures or techniques would be preferred in all        circumstances.    -   References to 1^(st) reasons for using particular structures or        techniques do not preclude other reasons or other structures or        techniques, even if completely contrary, where circumstances        would indicate that the 1^(st) reasons and structures or        techniques are not as compelling. In general, the invention        includes those other reasons or other structures or techniques,        especially where circumstances indicate they would achieve the        same effect or purpose as the 1^(st) reasons or structures or        techniques.

After reading this application, those skilled in the art would see thegenerality of this description.

Definitions

The general meaning of each of these terms or phrases is intended to beillustrative, and in no way limiting.

-   -   The phrase “access point”, the term “AP”, and the like,        generally refer to devices capable of wireless communication        with wireless devices, and capable of wireline communication        with other devices. In preferred embodiments, AP's communicate        with external devices using a L2/L3 network. However, in the        context of the invention, there is no particular requirement        that AP's have an actual wireline communication link; AP's might        communicate entirely wirelessly.    -   The phrase “multiple radios”, and the like, generally refers to        devices capable of wireless communication with wireless devices        while using multiple antennae, frequencies, or both.    -   The phrase “L2/L3 network”, and the like, generally refers to a        communication network in which data packets are transmitted in        accordance with the ISO/OSI model. In preferred embodiments, an        L2 network includes a LAN, such as an Ethernet-type LAN, while        an L3 network includes a packet-switched network, such as        multiple LAN's coupled using bridges or routers. However, as        noted below, in the context of the invention, where an L2/L3        network is described there is no particular requirement for any        particular type of network, whether designated as an L2/L3        network or otherwise.    -   The phrases “wireless device”, “wireless device”, and the like,        generally refer to devices capable of wireless communication        with AP's. In preferred embodiments, wireless devices implement        a wireless communication standard such as IEEE 802.11a, 11b, or        11g. However, in the context of the invention, there is no        particular requirement (1) that this particular communication        standard is used, e.g., the wireless communication might be        conducted according to a standard other than 802.11, or even        according to a an IEEE standard entirely, or (2) that all        wireless devices each use the same standard or even use        inter-compatible communication standards.    -   The phrase “wireless communication”, and the like, generally        refers to radio communication in a region of spectrum allocated        for that purpose, or for unlicensed use. In preferred        embodiments, wireless communication includes a wireless        communication standard such as IEEE 802.11a, 11b, or 11g.        However, in the context of the invention, there is no particular        requirement that wireless communication must necessarily (1) use        radio spectrum, (2) use electromagnetic communication, or        even (3) be entirely confined to untethered communication        coupling.

Personal cells and personal access points are techniques forcommunication between AP's and wireless devices over a communicationnetwork. In these techniques, a set of communication links are providedbetween AP's associated with the communication network and any wirelessdevices desiring contact with that communication network. Thecommunication links are operated according to a protocol in which eachwireless device select AP's with which to communicate. It should benoted that this is significantly different from cellular phone networksin which AP's select wireless devices with which to communicate.

In these techniques, the steps of operating include having a systemcoordinator select information sent by the AP's, with the effect thatwireless devices direct their communications to AP's chosen by thesystem coordinator. It should be noted that this is also different fromtypical operation of the 802.11 protocol, in which the wireless deviceswould chose which AP's with which to communicate.

Also in these techniques, multiple AP's provide an illusion to awireless devices that they are a single AP. An effect is that the needfor hard handoffs between AP's is lessened.

System Elements

FIG. 1 shows a block diagram of a wireless communication systemincluding access points and wireless devices.

Communication System

In one embodiment, a wireless communication system 100 includes elementsshown in the figure, including at least a system coordinator 110, asystem local network 120, a set of access points (“AP's”) 130, and a setof wireless devices 140.

The system coordinator 110 includes elements shown in the figure,including at least a coordinator circuit 111 and a coordinator database112. The coordinator circuit 111 includes a computing device, such as aprocessor, program and data memory, and optionally mass storage. Incases in which the coordinator circuit 111 includes a programmablecomputing device, it also operates under control of software, optionallydistinguished as operating system software and application software.

The coordinator database 112 includes information relating to the statusof the system 100, its AP's 130, and its wireless devices 140. Thisinformation preferably includes global state information about the AP's,the wireless devices, and the overall system. This information can becollected from the AP's and from the wireless devices through the AP's.The global state information can include, for example, which AP's arecommunicating with which wireless devices and parameters for thosecommunications. Examples of such parameters can include, but are notlimited to, identifiers and other data used by the AP's and wirelessdevices, signal strength and/or noise level information, and parameterssuch as data rate for the communications. The system coordinator canmake decisions based on global state information, for exampleinstructing AP's about what identifiers and other communicationparameters to use. The coordinator circuit 111 operates with thecoordinator database 112 to perform such functions, as described furtherbelow.

The system local network 120 includes any technique for sending andreceiving information between the system coordinator 110 and the AP's130. In a 1^(st) set of preferred embodiments, the system local network120 includes an L2/L3 network, capable of substantially reliablycommunicating data packets between the system coordinator no and theAP's 130. However, in the context of the invention, there is noparticular requirement for using this technique.

Wireless Device

Each wireless device 140 includes elements shown in the figure,including at least a device control circuit 141, a transmitter 142, anda receiver 143. In a 1^(st) set of preferred embodiments, the devicecontrol circuit 141 includes a computing device preprogrammed toimplement one or more of the IEEE 802.11a, 11b, or 11g protocols, andincludes one or multiple radios. One example of a wireless device couldbe a telephone or mobile computer preprogrammed to operate in a wirelessenvironment. However, in the context of the invention, there is noparticular requirement that the device control circuit 141 must bepreprogrammed; it may instead include programmable memory, data memory,and optionally mass storage. One example of this distinct type ofwireless device could be a mobile computer programmable to discover itswireless environment and operate therein.

Wireless devices make decisions regarding their communication based onlocal information, for example information about what AP's a wirelessdevice can “hear,” information about a communication link and possiblecommunication links sent by AP's to the wireless device, and the like.Wireless devices can choose an AP with which to communicate based onthis information.

In some circumstances, a wireless device might choose a sub-optimal APfor communication because it lacks global information about other AP's.The system coordinator can affect this choice by controllingcommunication parameters used by the AP's with respect to that wirelessdevice, thereby steering a wireless device's choice to a desired AP.

Access Points

In a preferred embodiment, each access point (AP) 130 includes elementsshown in the figure, including at least an AP control circuit 131, an APcontrol database 132, a transmit multiplexer 133, and a receivede-multiplexer 135.

The AP control circuit 131 includes a computing device, such as aprocessor, program and data memory, and optionally mass storage. Incases in which the AP control circuit 131 includes a programmablecomputing device, it also operates under control of software, optionallydistinguished as operating system software and application software.

The AP control database 132 includes information relating to the statusof the system 100, the particular AP 130, and those wireless devices 140assigned to that AP 130. The AP control circuit 131 operates with the APcontrol database 132 to perform functions described below.

The AP control circuit 131 determines which signals it desires to sendand on what frequencies, and sends that information to the transmitmultiplexer 133. The transmit multiplexer 133 causes those signals to bemultiplexed onto those frequencies using one or more radios. This systemallows wireless devices to associate with one frequency, as well asallowing wireless device devices that support “channel bonding”, i.e.,can support multiple frequencies simultaneously.

The receive de-multiplexer 135 causes the multiplexed signals to beseparated into their frequency-modulated information components, andcouples those information components to the AP control circuit 131.

After reading this application, those skilled in the art will realizethat combined operation of the AP control circuit 131, the transmittermultiplexer 133, and the receive de-multiplexer 135, have the effectthat the AP 130 can transmit or receive on any of its availablefrequencies. It is desirable for the AP 130, when sending and receiving,to not have its own transmission interfere with its own reception.

Personal Cell Model

In a personal cell model for a wireless communication system, anidentifier such as a BSSID is maintained at a plurality of AP's for eachwireless device. These AP's appear to each wireless device as if theywere a single AP that communicates with the wireless device using thatidentifier. A wireless device selects that single AP as the one withwhich it will communicate. The system coordinator selects one of theAP's for actually communicating with the wireless device, and mightchange that selected one of the AP's from time to time, without thewireless device having any knowledge. The remaining AP's can listenpassively to communication by the wireless device.

FIG. 2 shows one example of an embodiment including a personal cellmodel. The figure shows a first access point 210 and a second accesspoint 220. The figure also shows a set of three wireless devices 230,240, and 250 and a system coordinator 260. In the context of theinvention, there is no particular requirement for these particularnumbers of AP's and wireless devices; actual embodiments might havedifferent numbers, i.e., more or fewer, AP's and wireless devices.

Each AP maintains a data structure such as a data structure 270. Thedata structure 270 preferably includes a set of entries, each entrypreferably including an AP identifier, a value for a state of the AP, aset of identifiers for wireless devices (here shown as BSSIDs), a valuethat identifies the AP currently actively communicating with eachwireless device, and at least one value that indicates a received signalstrength indicator (RSSI), i.e., a measure of received signal strength,for that communication. The system coordinator 260 handles sharing ofinformation between AP's as needed to maintain the data structure 270 ateach AP.

In this example, all the relevant AP's in the system maintain theidentifier of each wireless device in the system. (In practice, onlythose AP's near to, i.e., within radio co-channel interference range of,the wireless device need actually maintain the identifier of anyparticular wireless device.) Any one of the AP's within radio range ofthe wireless device can actively communicate with any one of thewireless devices using the identifier for that wireless device. Theother AP's can passively listen to the communication so as to keep theirRSSI information up to date.

A first AP sends communications to the wireless device while one or moreAP's (possibly including the first AP) receive communications from thewireless device. One effect of this technique is that the wirelessdevice effectively sees only a single AP or with which it communicates,even though it might in reality be communicating with different AP's atdifferent times.

The system coordinator monitors each active wireless communication.Based on the characteristics of the communication, the systemcoordinator can determine which AP will be associated (or reassociated)with the wireless device for active communication. This is representedby the dashed lines in the figure between the system coordinator 260 andthe AP 210 and the AP 220.

In a preferred embodiment, the system coordinator considers multiplecharacteristics of the communication link between the AP's and thewireless device. These characteristics might include signal strength andother L0/L1 characteristics relating to the signal—the amount of noise,how “bursty” that noise is (whether noise occurs relatively evenly ornot), the type of noise (whether noise is concentrated on certainfrequencies, or other types of noise), the number of multipath images ofthe signal, and the like. These characteristics might include data rateand other L2/L3 characteristics relating to the communication link—thedata rate transmitted within a wireless LAN, the information throughputin a switched network, the ability to provide QoS to multiplerequestors, and the like. More generally, any characteristic ofcommunication the system coordinator can control by associating thewireless device with a particular AP of the system coordinator's choicemight be included in the communication characteristics used to determinehow to optimize handoff.

Changing the AP with which a wireless device is associated for wirelesscommunication is sometimes referred to as a “handoff” herein. Reasonsfor performing a handoff can include, but are not limited to, changes inRSSI data, optimizing load on wireless devices and/or AP's, changes incharacteristics of the communication, number of QoS flows, etc.

When the system coordinator determines that a particular AP shouldcommunicate with a particular wireless device, the system coordinatortells that AP to associate (or reassociate) itself with the wirelessdevice for active communication. The wireless device does not need totake any action. In other words, the handoff (sometimes called a “softhandoff” herein), generally occurs without the wireless device evenbeing aware of it. Preferably, no messages need to be exchanged betweenthe wireless device and the AP's to carry out the soft handoff. Rather,from the wireless device's point of view, nothing changes. Theinfrastructure of the system (i.e., system coordinator and AP's)preferably carries out the soft handoff entirely on its end.

An effect of this technique is that “hard handoffs”, i.e., handoffs ofwhich the wireless device is aware and which involve a handoff accordingto the communication protocol in use, and the communication delaysassociated therewith, can be minimized. Hard handoffs take more timethan soft handoffs; hard handoffs require messages to be exchangedbetween a wireless device and the AP's involved in the handoff. The morewireless traffic already present, the longer this message exchange cantake. This often results in a noticeable break in service. In contrast,as discussed above, the soft handoff enabled by the personal cell takesmuch less time and preferably are not even noticed or known about by thewireless device.

One reason the system coordinator might determine that a particular APshould communicate with a particular wireless device is that the RSSIfor that AP becomes better than the RSSI for an AP currently in activecommunication with the wireless device. This might occur, for example,if the wireless device moves.

A second reason the system coordinator might determine that a particularAP should communicate with a particular wireless device is that itchanges the interference pattern in the collection of AP's and wirelessdevices communicating in a shared wireless channel, with the intent ofoptimizing aggregate utilization of the shared spectrum. This mightoccur even if the wireless device does not move, but the communicationpattern of transmitters in the shared medium changes.

The possibility of a soft handoff provides for a new capability—a softhandoff between AP's that are co-located, or from a particular AP backto itself, might be performed. This provides the system coordinator withadditional tools for managing the set of communication links. Forexample, the system coordinator might perform load sharing acrossmultiple AP's. After reading this application, those skilled in the artwill recognize that other and further circumstances can arise whereinsoft handoffs are desirable.

The system coordinator might wish to force a wireless device to changeits identifier (e.g., the BSSID for that wireless device), even if itwishes to retain the same AP for communication with that particularwireless device. For a 1^(st) example, the system coordinator might wishto alter communication parameters with a particular wireless device. Fora 2^(nd) example, as described in more detail with regard to a “personalAP” model, the system coordinator might wish to assign that BSSID orother identifier to a different wireless device.

In changed communication conditions like or similar to those describedabove, the system coordinator might instruct an actively communicatingAP to force a hard handoff, in which the wireless device must select anew identifier. Hard handoffs might also be desirable in certaincircumstances related to the operation of a particular wirelesscommunication chipset such as the Atheros chipset.

In the IEEE 802.11 protocol, and possibly other protocols, AP'sadvertise their presence and availability to communicate usingparticular identifiers. In IEEE 802.11, messages by which the AP'sadvertise are called “beacons”. The protocol contemplates that each APwill have only a single identifier to advertise in each beacon. In manycircumstances, the AP is only concerned with sending the information inthe beacons to a single wireless device, or a chosen set of wirelessdevices. As a result, the data rate for the beacons can be maximized forthat particular set of AP/wireless device communication.

In some embodiments, it might be possible to combine beacons (sometimescalled “coalescing”). In these embodiments of the invention, (1) each APmight advertise multiple identifiers in one beacon, (2) each AP mightalter the communication parameters for its beacon, such as for exampledata rate or signal strength, to account for the number of identifiersin that beacon, and (3) each AP might customize the information in itsbeacon for each one of the multiple identifiers, such as for exampleindicating specific communication parameters for each such identifier,whether all in the same beacon or in distinct beacons. Thesecommunication parameters can include, but are not limited to, accesscontrol parameters, backoff or retry parameters, channel selectionparameters, quality of service parameters, and transmit power parameters

The system coordinator preferably has sufficient information, forexample the communication parameters and the RSSI data between each APand each wireless device, to customize the beacon messages so as tolessen interference with other communications. In addition, the numberof messages sent can be responsive to such RSSI data and to a number ofthe identifiers to be sent. For a large number of identifiers, moremessages can be sent so that each message interferes less with othercommunications (i.e., uses less communication bandwidth).

Personal Access Point Model

In a personal access point model, each wireless device is associatedwith a substantially unique identifier, such as a substantially uniqueBSSID. Identifiers are only “substantially” unique, in that it ispossible that identifiers are reused elsewhere where radio co-channelinterference is substantially nil. In preferred embodiments, whenwireless devices with equal or equivalent identifiers enter a regionwhere co-channel interference is no longer insignificant, the systemcoordinator preferably attempts to change at least one of thoseidentifiers. Each particular wireless device has its substantiallyunique identifier associated with substantially only one of a pluralityof AP's to enable communication between that AP and the wireless devicewith that identifier, specifically, the one AP the system coordinatorselects for communication with the wireless device.

FIG. 3 shows one example of a personal AP model. The figure shows afirst AP 310 and a second AP 320. The figure also shows a set ofwireless devices 330 and 340 and the system coordinator 360. In thecontext of the invention, there is no particular requirement for theseparticular numbers of AP's and wireless devices; actual embodimentsmight have different numbers, i.e., more or fewer, AP's and wirelessdevices.

The AP's preferably maintain data structures such as data structure 370.This data structure is explained in more detail below with reference toFIG. 4, FIG. 5, and FIG. 6. Generally, the data structure describes anassociation between a particular AP with one or more identifiers (e.g.,BSSID's) for one or more selected wireless devices. This association ispreferably limited to those AP's that are going to actively communicatewith those selected wireless devices.

When a wireless device needs to communicate with a different AP, thewireless device's identifier is associated or reassociatied with thatother AP. This is unlike other wireless systems in which the wirelessdevice would have to change its identifier in order to communicate witha new AP through a hard handoff. For a 1^(st) example, the wirelessdevice might have moved, and no longer has a good communication linkwith its former AP. For a 2^(nd) example, the system coordinator mightdesire to move the wireless device's association to a different AP forload balancing. After reading this application, those skilled in the artwill recognize that this technique has other and further uses.

The system coordinator 360 preferably controls these steps ofassociating or reassociating by instructing or providing information tothe AP's so that they change the associated identifiers in their datastructures 370. This is illustrated by the dashed lines between thesystem coordinator 360 and the AP's 310 and 320 in the figure.

In the personal AP model, the set of communication links appears to thewireless device identical to the personal cell model. The wirelessdevice does not need to take any action when the system coordinatormoves its association to another AP. Similar to the personal cell model,a soft handoff preferably occurs without the wireless device having anyknowledge thereof. Rather, the infrastructure of the system (i.e.,system coordinator and AP's) preferably carries out the soft handoffentirely on its end. Also similar to the personal cell model, one effectof this technique is that hard handoffs and their associatedcommunication delays can be minimized.

Similar to the personal cell model, soft handoffs might be used when awireless device moves so that another AP is better situated tocommunicate with the wireless device (for example, as reflected by RSSIdata, load optimization considerations, changes in characteristics ofthe wireless communication, number of QoS flows, etc.). Also similarly,situations may arise where a soft handoff between co-located AP's isdesirable. Changes in other communication conditions might warrant asoft handoff. After reading this application, those skilled in the artwill recognize that this technique has other and further uses. Alsosimilar to the personal cell model, it might be desirable to force ahard handoff in some cases.

In the foregoing descriptions of FIGS. 2 and 3, a BSSID was used as anexample of the identifier. However, identifiers are not limited to justBSSID's. Other identifying data such as a mobility domain can be used aspart of the identifier. One example of such an identifier is describedbelow with reference to FIGS. 4 and 5. Identifiers of completelydifferent types that do not include mobility domains or BSSID's are alsowithin the scope of the invention.

Data Structures for Personal Access Point

In one embodiment, each wireless device is assigned an identifier asdescribed with respect to FIG. 4 and FIG. 5. FIG. 4 shows an identifierassigned to a wireless device. FIG. 5 shows a pair of data structuresused by an AP.

An identifier 400 includes a sequence of individual bits 401, preferably48 such bits 401 as would be used to describe a MAC address or BSSID.When used to describe a MAC address or BSSID, a 1^(st) (two bit) section402 of those individual bits 401 are substantially permanently set to“00” (two zero bits), with the effect that the identifier 400 can berecognized as a MAC address or BSSID.

A 2^(nd) section 403 of those individual bits 401 are set to a valuedescribing a mobility domain 404. In a preferred embodiment, the 2^(nd)section 403 includes two to three individual bits 401; however, in thecontext of the invention there is no particular requirement for usingthis number of individual bits 401, and other or different numbers mightbe used. Moreover, in the context of the invention there is noparticular requirement for this number of individual bits 401 to befixed; the number of individual bits 401 might be dynamically maintainedby the AP at the direction of the system controller, or otherwise.

In one embodiment, a mobility domain 404 indicates a logical or physicalregion in which wireless devices are expected to be present. The systemcontroller recognizes wireless devices that leave a 1^(st) mobilitydomain 404 and enter a 2^(nd) mobility domain, and causes them to bereassigned to a new identifier 400. This typically involves a hardhandoff, in which the wireless device is instructed to deassociate fromthe earlier identifier 400 and newly associate with the new identifier400.

In cases in which a mobility domain 404 indicates a physical region,this has the effect that wireless devices physically crossing a boundarybetween a 1^(st) and a 2^(nd) physical region, each associated with aparticular mobility domain 404, leave a 1^(st) mobility domain 404 andenter a 2^(nd) mobility domain 404. In cases in which a mobility domain404 indicates a logical region, this has the effect that wirelessdevices might be reassigned from a 1^(st) to a 2^(nd) mobility domain404 without necessarily moving across a physical boundary between twomobility domains 404.

Mobility domains also can be assigned to channels, for example with onemobility domain per channel. Seamless mobility is thereby enhancedbecause load on the channel over a coverage area can be optimized.

As described below, using a mobility domain 404 to indicate logicalregions as well as, or instead of, physical regions, provides the systemcontroller with the ability to logically move wireless devices, bothamong AP's and otherwise. For a 1^(st) example, the system controllermight move wireless devices from a 1^(st) to a 2^(nd) mobility domain404 for load sharing. For a 2^(nd) example, the system controller mightmove wireless devices from a 1^(st) to a 2^(nd) mobility domain 404 toalter their parameters for communication with AP's. For a 3^(rd)example, as described below, the system controller might move wirelessdevices from a 1^(st) to a 2^(nd) mobility domain 404 to account forthose cases in which there is a conflict between identifiers 400assigned to distinct wireless devices, as also described below and inmore detail with respect to FIG. 6 and FIG. 7.

The identifier 400 includes a 3^(rd) section 405 of those individualbits 401, in which ones and tuples of those individual bits 401 areassigned to particular wireless devices. As also described below and inmore detail with respect to FIG. 6 and FIG. 7, each wireless deviceentering the radio co-channel interference range of an AP and itsneighbors (the AP's “radio zone” 405) is assigned one of thoseindividual bits 401 as its substantially unique identifier 400. Asadditional wireless devices enter the AP's radio zone 405, each one isassigned a distinct one of those individual bits 401 as itssubstantially unique identifier 400. When the ones of those individualbits 401 are all allocated, additional wireless devices entering theAP's radio zone 405 might be assigned to distinct mobility domains 404at the same AP, with the effect of substantially distinguishing theiridentifiers 400 from those of all other wireless devices in the AP'sradio zone 405.

If there are two bits in the 2^(nd) section 403, there will be 2²defined mobility domains 404, and 48−2−2 (i.e.) 44) defined individualbits 401 allocated to wireless devices, for a combination of 176distinct identifiers supported by a single AP. If there are three bitsin the 2^(nd) section 403, there will be 2³ defined mobility domains404, and 48−2−3 (i.e., 43) defined individual bits 401 allocated towireless devices, for a combination of 344 distinct identifierssupported by a single AP. The number of bits reserved for the 2^(nd)section and defining mobility domains 404 is preferably dynamicallydetermined by the system controller.

If additional wireless devices enter the AP's radio zone 405 and thoseadditional wireless devices all wish to communicate with the same AP,the system controller might safely assign them the same identifiers 400as other wireless devices communicating with the same AP. At worst case,two wireless devices nearly simultaneously communicating with the sameAP will cause a data collision, requiring no more than backoff and laterretransmission.

If still more additional wireless devices enter the AP's radio zone 405,the system controller might safely lock one or more of those individualbits 401, with the effect that each such wireless device newly enteringthe AP's radio zone can be assigned a bit-tuple 406 (a bit-pair when onebit is locked, a bit-triple when two bits are locked, and the like).Each time a bit-tuple 406 of length V is generated, a number equal to(2^(v)−1)−V new identifiers become available for the system controllerto assign to wireless devices. However, when a bit-tuple 406 is assignedto a wireless device, its individual bits 401 should not be reassigneduntil that particular wireless device is the only wireless device usingthat bit-tuple 406. In the event the system controller wishes toreassign those individual bits 401 without waiting for this condition,the system controller might cause a hard handoff by the wireless device,and assign it to a new substantially unique identifier 400.

As described above, FIG. 5 shows a pair of data structures used by an APin one embodiment of the invention.

First data structure 501 is a bit map such as the Atheros (chipset)BSSID. Second data structure 502 is a mask. If a wireless device with anidentifier attempts to communicate with an AP with a given bit map and agiven mask, the AP will acknowledge the attempt if the following istrue:identifier AND mask=bitmap  (1)

The bitmap is generally set to all 0s, except as noted below. Thisequation has the effect of masking out (by ANDing with 0) any unusedbits in the mask. Thus, wireless devices with identifiers that have a 1corresponding to an unused bit are acknowledged.

In the case of the Atheros chipset and a BSSID used as a wirelessdevice's identifier, equation (1) is equivalent to the following:BSSID (of wireless device) AND mask=Atheros BSSID  (2)

If a wireless device with a given identifier is acknowledged, the maskis updated as follows:mask=mask OR identifier  (3)

This has the effect of updating the mask so that a wireless device witha same identifier as a wireless device that has already beenacknowledged will not satisfy equation (1) above.

Data structure 502 in FIG. 5 indicates fields for the mask according toan embodiment of the invention. This embodiment can be used with theAtheros chipset and BSSIDs (including mobility domains). Applicabilityto other chipsets, identifiers, and different lengths of bit fieldswould be apparent to one skilled in the art.

In one embodiment, the 1^(st) (two bit) section of the mask is set tozeros, which correspond to the first (two bit) section of wirelessdevices' identifiers discussed above with respect to FIG. 4. The 2^(nd)(two bit) section corresponds to the mobility domain. The 3^(rd) (44bit) section corresponds to 44 wireless devices if one bit of thesection is used for each wireless device.

The identifiers and masks can be adapted to accommodate more than 44wireless devices. In particular, if more wireless devices are needed, abit of the 3^(rd) (44 bit) section of the identifier can be “pinned” toa particular access point. In other words, wireless devicescommunicating with that access point will have that bit set to a 1 aswell as their own identifying bit.

In cases in which all wireless device identifiers associated with the APhave a 1 at the pinned bit, the mask will have a 1 at the pinned bitwhen checking equation (1) for received messages. In order that equation(1) can still be satisfied for those wireless devices at the APcorresponding to the pinned bit, the bitmap for that AP is modified byplacing a 1 at the location of the pinned bit.

The pinned bit is no longer available for identifying a particularwireless device. Different bits can be set for different access points.As described above, an effect is that when a V^(th) bit is “pinned” toan access point, 2^(v)−v−1 possibilities for wireless devices are added.Thus, sufficient wireless devices can be accommodated for a great manyapplications.

The mask is automatically updated by equation (3) above to accommodatethe pinned bit(s). Therefore, the operation of the access point can beadapted to use “pinned” bits with relative ease.

The assignment of identifiers to wireless devices, and if necessary, thepinning of bits at the wireless devices and the AP preferably arecontrolled by the system coordinator. An effect of this is that thesystem coordinator can control which wireless devices communicate withwhich APs.

Initial Assignment of Identifier

For each AP radio, the system coordinator preferably maintains a set ofother AP radios with which it interferes. For each AP radio, the systemcoordinator maintains a vector of assignments (ASV), where each bit inthe ASV denotes the corresponding ‘1’ in the identifier (e.g., BSSID) ofthe personal AP allocated for a wireless device that is assigned by thesystem coordinator to the AP radio. For each AP radio, the systemcoordinator maintains an availability vector (AVV), where each bit inthe AVV denotes that a conflict free identifier may be constructed withonly the corresponding bit set to ‘1’.

When a wireless device comes into a preferred embodiment of the system,it first looks for access points and sends a “probe request” message.Every AP in the neighborhood of the wireless device receives thismessage. The “probe request” message triggers a “probe indication”message from the AP to the system coordinator. When the systemcoordinator receives a probe indication from an AP for a wirelessdevice, it needs to generate a identifier for that device, so thatfuture communications can take place with the said device on theselected identifier. The following are the rules preferably used forgeneration of the identifier:

-   -   1. If there is a bit available in the AVV, construct a        identifier by randomly selecting a bit from the AVV, and        prefixing with the mobility domain. This device has been        allocated its personal AP.    -   2. If there is no bit available in the AVV, check to see if        there is an identifier to which multiple devices have already        been allocated. If so, provide this identifier to the device.        This device has been allocated a shared identifier.    -   3. If there is no such identifier above, check to see if there        is a identifier sharing the same SSID (or network service) that        the new device has. If so, convert that identifier from a        personal AP to a shared AP. The incoming device has been        allocated a shared AP, and some existing device in the network        also has its personal AP converted to a shared AP.    -   4. If there is an existing shared identifier (i.e. a identifier        with more than one ‘1’ except for the mobility domain) that is        available for allocation, select it. This device has been        allocated a shared AP.    -   5. If there is no identifier available in the shared pool, then        increase the number of ‘1’ bits in the identifier from the set        of assigned pool of identifiers. This will create new        identifiers in the shared pool. Select one identifier from the        shared pool, and allocate to the device. This device has been        allocated a shared AP.        Conflicts Between Identifiers

FIGS. 6 and 7 show conceptual diagrams of two cases that can result inhard handoffs between wireless devices using personal access points.

In FIG. 6, mobile device 610 is actively communicating with access point620, and mobile device 630 is actively communicating with access point640. The circles around the access points indicate their effective rangefor communicating with the mobile devices.

In this example, both mobile devices have the same identifier forcommunication with their associated access point. This would not be aproblem except that mobile device 610 has moved within the effectiverange of access point 640. Thus, mobile device 610 has two AP's in itsneighborhood, AP 620 and AP 640, with the same. This causes both theAP's to acknowledge transmissions from mobile device 610, therebycausing collisions. This will force a deauthorization of one of themobile devices, which will then have to get a new identifier through ahard handoff. The hard handoff to a new identifier preferably is undercontrol of the system coordinator.

In FIG. 7, mobile device 610 is actively communicating with access point620, and mobile device 630 is actively communicating with access point640. Access point 650 is also present in the system. Again, the circlesaround the access points indicate their effective range forcommunicating with the mobile devices.

In this example, both mobile devices have the same identifier forcommunication with their associated access point. Furthermore, neithermobile device is within the effective range of the access pointassociated with the other mobile device. However, a problem still canarise if both mobile devices are within the effective communicationrange of another access point. This is illustrated in FIG. 7, where bothmobile devices 610 and 630 are within the effective range of accesspoint 650.

Even though access point 650 is not actively communicating with eithermobile device, it still may be passively listening, sending beaconmessages, and the like. In addition, one or both of the mobile devicesmay have a soft handoff to the access point 650. Thus, having multipleAP's with the same identifier in the range of a mobile device is notdesirable. A system coordinator preferably will recognize this problemand force a hard handoff of one of the mobile devices to a newidentifier.

Soft Handoff and Hard Handoff

In a preferred embodiment, the system coordinator periodically executesan algorithm to make its handoff decisions. In this periodic check, thesystem coordinator preferably does the following:

-   -   1. For each wireless device, the system coordinator determines        if there is any conflict for that wireless device, i.e. if there        exist two AP's in its interference range that have the same        BSSID to which that particular wireless device is communicating.        If the system coordinator determines that such a conflict        exists, it may preferably deassociate the wireless device and        cause a hard handoff to a different BSSID to eliminate the        conflict.    -   2. For each wireless device, the system coordinator determines        if there is an AP neighbor that is better suited to serve the        device (e.g. it has a better RSSI for the device), and to which        the current BSSID of the device can be transferred without        creating conflict for (a) the said device, or (b) any of the        devices that are within the interference range of the said AP.        If so, the system coordinator can execute a “soft handoff” to        the best such AP neighbor.    -   3. For each wireless device, the system coordinator determines        if the current service is poor (e.g. RSSI lower than a        configured threshold, or significant loss of messages between        the wireless device and its communicating AP), and if there is a        significantly superior AP that can serve the device (e.g. it has        significantly better RSSI for the device). In this case, even if        the soft handoff criterion described above fails, the system        coordinator may preferably initiate a “hard handoff” by        disassociating the device from its current AP and only allowing        it to enter the new AP on a different BSSID.        Clock Synchronization

In both the personal AP model and the personal cell model, multiple AP'sare providing an illusion to wireless devices that they are a single AP.In a preferred embodiment of the system, the clocks of the AP's shouldbe synchronized in order to facilitate proper communications. The AP'smonitor common wireless devices and record their packet reception times.These packet reception times, along with corresponding packet IDs, aresent to the system coordinator. This allows the system coordinator tomaintain a digest of clock offsets, and to signal back to each AP toadjust its clock offset, with the effect of synchronizing the AP clocks.One effect of this is that even when a wireless device sees two beaconsfrom different AP's, no time mismatch or only a negligible time mismatchis present.

Beacon Synchronization

In a preferred embodiment, the system coordinator also synchronizesseveral beacon parameters. For example, 802.11 has a mechanism whereinwireless devices can go into power-save mode, and wake up onlyperiodically to monitor a beacon. When there is a packet for a wirelessdevice in power-save mode, the AP buffers the packet. The beacon packethas a field where it identifies which wireless devices have packetsbuffered for them. The wireless devices can then request to receivethese buffered packets. Because the wireless device believes that it iscommunicating with only one AP, when in fact it might be communicatingwith more than one AP that are providing the illusion of being a singleAP, the wireless device might latch onto a beacon from an AP other thanthe one buffering its messages. Beacon information among the AP's ispreferably synchronized. This has the effect of helping buffered packetsget to wireless devices when they wake up.

Generality of the Invention

This invention should be read in the most general possible form. Thisincludes, without limitation, the following possibilities includedwithin the scope of, or enabled by, the invention.

-   -   Communication throughput using AP's can be substantially        increased, much closer to the maximum theoretical capacity in        the case where each AP uses the entire available wireless        spectrum.    -   Handoff of wireless devices from a 1^(st) AP to a 2^(nd) AP can        be substantially sped up, much closer to the minimum theoretical        time for the system to find a superior AP for a moving wireless        device, and to reassign (reassociate) that wireless device to a        new AP.    -   Soft handoff between two AP's can be accomplished without any        messaging with the mobile device, thereby making the handoff        time independent of the amount of traffic over the communication        channel.    -   Handoffs between frequencies on a same access point are enabled.    -   Alternative embodiments are also applicable to non-802.11        protocols, and are particularly useful in environments where the        digital protocol involves commutativity of channels between        transmitter and receiver.    -   Alternative embodiments provide for deployment of co-located        AP's that support multiple frequencies. This has the effect of        providing for better handoff, with the effect of making        deployment much easier. Optimization occurs primarily across        frequencies and not across both frequencies and substantially        spatial distances.    -   Alternative embodiments might provide for simultaneous        optimization of both peak and aggregate throughput; in the        context of the invention, there is no particular requirement for        frequency planning across AP's.    -   Alternative embodiments support different radios having        different transmit power and receive power, with the effect of        providing different coverage planning on different channels.    -   Alternative embodiments provide for radios to perform collision        detection in a broadcast wireless medium. With the 802.11 packet        handshake detecting frame-level collision, the invention        provides for reception on the same channel while transmitting,        with the effect that recovery from collisions is relatively        faster.    -   Alternative embodiments provide for use of CSMA/CD protocols as        well as CSMA/CA protocols.    -   Advantages of the invention include:        -   1. The ability to hand off without any over the air            messages.        -   2. Achieving handoff times that are independent of the            amount of traffic on the communication channel.        -   3. The ability to perform load balancing transparent to the            clients.        -   4. Support for different client implementations in a single            infrastructure, optimizing handoffs for all clients equally,            regardless of client implementations or algorithms.        -   5. Ability to optimize channel parameters (particularly data            rates) for clients.

After reading this application, those skilled in the art would see thegenerality of this application.

The invention claimed is:
 1. A computer-implemented method in a systemcoordinator to provide seamless mobility to an end point in a wirelessnetwork by controlling soft handoffs of the end point among accesspoints with the use of a persistent, uniquely-assigned BSSID (BasicService Set Identifier), comprising: selecting at least onecommunication parameter to associate with a BSSID; sending a beacon froma first access point to advertise its presence, wherein the beaconcomprises the BSSID associated with the at least one communicationparameter; responsive to the mobile station choosing the BSSID beingadvertised in the beacon sent from the first access point, selecting touniquely assign the BSSID to a mobile station; associating the firstaccess point from the plurality of access points with the mobilestation, wherein associating comprises using the uniquely-assigned BSSIDwith the mobile station persistently and associating is made as selectedby the system coordinator, the uniquely assigned BSSID being independentof an identify of mobile station and being eligible for subsequentassignment to a different mobile station as determined by the systemcoordinator; determining that the mobile station should be handed-offfrom the first access point to a second access point among the pluralityof access points; handing-off the mobile station by changingassociations of the uniquely-assigned BSSID from the first access pointto a second access point, wherein a coordinator database of the systemcoordinator is updated according to the change, the coordinator databasestoring a plurality of access point identifiers in association with aplurality of mobile station identifiers, wherein the uniquely-assignedBSSID is persistent due to the mobile station maintaining the uniquelyassigned BSSID through hand-offs between access points; and responsiveto the hand-off, seamlessly continuing communication with the mobilestation at the second access point while using the sameuniquely-assigned BSSID without change at the mobile station, such thatthe mobile station continues communication with the second access pointas if communication was still occurring with the first access point. 2.The method of claim 1, wherein associating the mobile station comprises:associating the mobile station with the first access point in a wirelessnetwork using the uniquely-assigned BSSID among a plurality of storeduniquely assigned BSSIDs assigned to a plurality of mobile devices. 3.The method of claim 1, wherein associating the mobile station comprises:associating the mobile station with the first access point in a wirelessnetwork using the uniquely-assigned BSSID among a plurality of storeduniquely assigned BSSIDs assigned to a plurality of mobile devices,wherein the plurality of stored uniquely-assigned BSSIDs are stored atthe first access point to facilitate communication between the firstaccess point and the plurality of mobile devices.
 4. The method of claim1, wherein associating the mobile station comprises: associating themobile station with the first access point among the plurality of accesspoints in the wireless network using the BSSID that is uniquely assignedto the mobile station, wherein the mobile station operates according toa protocol in which the mobile station natively selects access pointswith which to communicate.
 5. The method of claim 1, wherein associatingthe mobile station further comprises: associating the mobile stationwith the first access point, wherein the mobile station is within rangeof at least two access points of the plurality of access points.
 6. Themethod of claim 1, wherein handing-off the mobile station comprises:disassociating the mobile station by deleting the uniquely-assignedBSSID stored at the first access point in favor of associating themobile station by storing the uniquely-assigned BSSID at the secondaccess point.
 7. The method of claim 1, wherein handing-off the mobilestation comprises: responsive to a change in location of the mobiledevice, handing-off the mobile station.
 8. The method of claim 1,wherein handing-off the mobile station further comprises: responsive toload optimization among components of the wireless network, from aglobal perspective of all mobile devices and all access points,handing-off the mobile station from the first access point to the secondaccess point.
 9. The method of claim 1, wherein handing-off the mobilestation further comprises: responsive to QoS (quality of service)requirements, handing-off the mobile station.
 10. The method of claim 1,wherein handing-off the mobile station further comprises: responsive toglobal state information concerning components in the wireless network,handing-off the mobile station.
 11. The method of claim 1, furthercomprising: sending the beacon from the first access point to advertiseits presence, wherein the beacon comprises multiple BSSIDs.
 12. Themethod of claim 1, wherein the at least one communication parametercomprises at least one of access control, a backoff or retry parameter,a channel selection parameter, quality of service, and transmit power.13. The method of claim 1, wherein selecting the first access point fromthe plurality of access points comprises: selecting the first accesspoint from the plurality of access points based on characteristics ofcommunication by the mobile station.
 14. The method of claim 1, whereindetermining that the mobile station should be handed-off from the firstaccess point to the second access point among the plurality of accesspoints: determining that the mobile station should be handed-off fromthe first access point to the second access point among the plurality ofaccess points to change an interference pattern of the plurality ofaccess points for optimizing aggregate utilization of a shared spectrum.15. The method of claim 1, further comprises the uniquely-assigned BSSIDfrom a plurality of persistent, uniquely-assigned BSSIDs to associatewith the mobile station based on one or more communication parameters ofthe uniquely-assigned BSSID selected from the group of: access controlparameters, backoff or retry parameters, channel selection parameters,QoS parameters, and transmit power parameters.
 16. Acomputer-implemented method, comprising: selecting at least onecommunication parameter to associate with a BSSID (Basic Service SetIdentifier); sending a beacon from an access point to advertise itspresence, wherein the beacon comprises the BSSID associated with the atleast one communication parameter; uniquely assigning the BSSID to amobile station, the BSSID being advertised in the beacon and beingindependent of an identity of the mobile station for subsequentassignment of a different mobile station; associating a mobile stationwith a first access point among a plurality of access points in awireless network for communication using the uniquely assigned BBSIDhanding-off the mobile station by changing associations from the firstaccess point to a second access point among the plurality of accesspoints; responsive to the hand-off, seamlessly continuing communicationwith the mobile station at the second access point while using the sameuniquely-assigned BBSID without change at the mobile station; changingat least one communication parameter to associate with the mobilestation; and forcing the mobile station to select a different BSSIDassociated with the changed communication parameter.
 17. A computerimplemented method, comprising: selecting at least one communicationparameter to associate with a BSSID; sending a beacon from a firstaccess point to advertise its presence, wherein the beacon comprises theBSSID associated with the at least one communication parameter; uniquelyassigning the BSSID (Basic Service Set Identifier) to a mobile station,the BSSID being advertised in the beacon and being independent of anidentity of the mobile station for subsequent assignment of a differentmobile station, wherein the uniquely assigned BSSID is unique to theextent that no range overlap exists between access points from aplurality of access points which use the same uniquely-assigned BSSID;associating the mobile station with the first access point among theplurality of access points in a wireless network for communication usingthe uniquely-assigned BSSID; handing-off the mobile station by changingassociations from the first access point to a second access point amongthe plurality of access points; responsive to the hand-off, seamlesslycontinuing communication with the mobile station at the second accesspoint while using the same uniquely-assigned BSSID without change at themobile station; responsive to conflict between mobile devices using thesame uniquely-assigned BSSID, reassigning at least one of the mobiledevices to an updated uniquely-assigned BSSID.
 18. At least onenon-transitory computer readable medium storing a computer programproduct that when executed by a processor performs a method in a systemcoordinator to provide seamless mobility to an end point in a wirelessnetwork by controlling soft handoffs of the end point among accesspoints with the use of a persistent, uniquely-assigned BSSID (BasicService Set Identifier), comprising: selecting at least onecommunication parameter to associate with a BSSID; sending a beacon froma first access point to advertise its presence, wherein the beaconcomprises the BSSID associated with the at least one communicationparameter; responsive to the mobile station choosing the BSSID beingadvertised in the beacon sent from the first access point, selecting touniquely assign the BSSID to a mobile station; associating the firstaccess point from the plurality of access points with the mobilestation, wherein associating comprises using the uniquely-assigned BSSIDwith the mobile station persistently and associating is made as selectedby the system coordinator, the uniquely assigned BSSID being independentof an identify of mobile station and being eligible for subsequentassignment to a different mobile station as determined by the systemcoordinator; determining that the mobile station should be handed-offfrom the first access point to a second access point among the pluralityof access points; handing-off the mobile station by changingassociations of the uniquely-assigned BSSID from the first access pointto a second access point, wherein a coordinator database of the systemcoordinator is updated according to the change, the coordinator databasestoring a plurality of access point identifiers in association with aplurality of mobile station identifiers, wherein the uniquely-assignedBSSID is persistent due to the mobile station maintaining the uniquelyassigned BSSID through hand-offs between access points; and responsiveto the hand-off, seamlessly continuing communication with the mobilestation at the second access point while using the sameuniquely-assigned BSSID without change at the mobile station, such thatthe mobile station continues communication with the second access pointas if communication was still occurring with the first access point. 19.A system coordinator to provide seamless mobility to an end point in awireless network by controlling soft handoffs of the end point amongaccess points with the use of a persistent, uniquely-assigned BSSID(Basic Service Set Identifier), comprising: a first module to select atleast one communication parameter to associate with a BSSID; a secondmodule to send a beacon from a first access point to advertise itspresence, wherein the beacon comprises the BSSID associated with the atleast one communication parameter; a third module to responsive to themobile station choosing the BSSID being advertised in the beacon sentfrom the first access point, select to uniquely assign the BSSID to amobile station; a fourth module to associate the first access point fromthe plurality of access points with the mobile station, whereinassociating comprises using the uniquely-assigned BSSID with the mobilestation persistently and associating is made as selected by the systemcoordinator, the uniquely assigned BSSID being independent of anidentify of mobile station and being eligible for subsequent assignmentto a different mobile station as determined by the system coordinator; afifth module to determine that the mobile station should be handed-offfrom the first access point to a second access point among the pluralityof access points; a sixth module to hand-off the mobile station bychanging associations of the uniquely-assigned BSSID from the firstaccess point to a second access point, wherein a coordinator database ofthe system coordinator is updated according to the change, thecoordinator database storing a plurality of access point identifiers inassociation with a plurality of mobile station identifiers, wherein theuniquely-assigned BSSID is persistent due to the mobile stationmaintaining the uniquely assigned BSSID through hand-offs between accesspoints; and a seventh module to responsive to the hand-off, seamlesslycontinue communication with the mobile station at the second accesspoint while using the same uniquely-assigned BSSID without change at themobile station, such that the mobile station continues communicationwith the second access point as if communication was still occurringwith the first access point.